1. Technical Field
Embodiments disclosed herein generally relate to the measurement of fluid properties. In particular, the disclosed embodiments are related to determining a density of a fluid using a single magnet fluid densitometer.
2. Description of Related Art
There are many instances in industrial processes and controls for handling flowing fluids where the density of the moving fluid has to be determined accurately. One particular application is in the identification of reservoir fluids flowing in a well such as in a pumpout wireline formation tester (PWFT) or logging while drilling formation tester (LWDFT) used to collect reservoir fluid samples in a well drilled for hydrocarbon exploration. The in-situ determination of fluid density under reservoir conditions is of vital importance in formation evaluation. Water often co-exists with gaseous hydrocarbons and crude oil in some common geologic formations. As such, a mixture of water, gaseous hydrocarbons, and liquid hydrocarbons is often produced by a working oil well, and the mixture is ultimately separated at a downstream location. It is often desirable to determine the amount of oil that is produced in a stream flowing from a formation. Because the amount of oil produced in the stream will influence the density of the fluid, measuring the density of the fluid can provide a reasonable estimation as to the amount of oil in the fluid.
One example of a densitometer that can be used to measure the density of an unknown process fluid is a Coriolis mass flowmeter, such as disclosed in U.S. Pat. No. 4,491,025, issued to Smith et al. A Coriolis mass flowmeter may contain two parallel conduits, each typically being a U-shaped flow tube wherein each flow tube is driven such that it oscillates about an axis causing each tube to twist about a torsional axis to produce a slight deformation and deflection of the conduit proportional to the mass flow rate of the fluid. This deformation is normally measured as a small difference between the deflection at the inlet ends of the conduits compared to the deflection at the outlet ends. Both tubes are oppositely driven such that each tube behaves as a separate tine of a tuning fork and thereby cancels any undesirable vibrations that might otherwise mask the Coriolis forces. The resonant frequency at which each flow tube oscillates depends upon its total mass, i.e. the mass of the empty tube itself plus the mass of the fluid flowing therethrough. Inasmuch as the total mass will vary as the density of the fluid flowing through the tube varies, the resonant frequency will likewise vary with any changes in density.
Another example of a densitometer is discussed in U.S. Pat. No. 4,491,009, issued to Reusch, wherein the density of an unknown fluid flowing through an oscillating flow tube is proportional to the square of the period at which the tube resonates. A further exemplary densitometer is disclosed in U.S. Pat. No. 6,378,364, by Pelletier et al., which is assigned to the same assignee as the present disclosure. Therein, a measurement device compares vibration frequencies from a sample cavity and a reference cavity to determine desired fluid properties.
However, due to the limited space in downhole applications, in most of the densitometers described above, the transmitter or driver is often located in close proximity to the receiver and may cause interference between the two components. The interference may distort the signal picked up on the receiver and cause difficulty in accurately recognizing the vibratory response of the flow tube. Thus, many of the prior art methods have used multiple flow tubes to create a reference point to cancel out external interference.
Consequently, there is a need for a high-accuracy densitometer which is capable of operation under the high temperature, pressure, shock and vibration conditions encountered in a wellbore. There is also a need for a densitometer which allows for a greater ease of construction and improved sensitivity over existing densitometers. Furthermore, there is a need for a device that not only is capable of determining a density of a fluid, but can also simultaneously determine other properties of a fluid, such as a fluid pressure and a fluid viscosity.